We anticipate continuing our kinematic studies of multiple simultaneous displacement patterns of walking of patients with specific arthritis and neurological disabilities and comparing their disordered walking performance with standards of normal variability which we have established previously. We also will measure the nature and amount of assistance required for walking, utilizing force-recording canes and crutches. We have developed methods to obtain quantitative measurements of basic mechanisms which are operable in the causation of gait abnormalities and have begun to establish the ranges of normal variability for these mechanisms which will serve as baselines for comparing the deficits in disabled patients. These mechanisms include: muscle weakness, muscle rigidity and spasticity, joint immobility, and postural unsteadiness and upright instability. In a multi-faceted approach we plan to study patients with severe arthritis before and after various types of major reconstructive surgery and compare the effect of different types of total hip and knee arthroplasties on various components of function such as walking performance, cane force, muscle strength, joint mobility, and weight- supporting activity. We plan to continue studying the interrelationship between muscle spasticity, rigidity, or weakness, postural steadiness and upright stability, and walking performance in patients with Parkinson's disease and hemiparesis following stroke. We will measure the effect of various approved drugs directed toward reducing spasticity and also the effect of various approved drugs directed toward reducing spasticity and also the effect of various braces on their walking performance.